Air liquefaction separation method and apparatus

ABSTRACT

Disclosed is an air liquefaction separation method and apparatus by which the apparatus cost can be reduced when liquid products are collected, the method including:
         a feed air compression step in which the whole amount of a feed air is a pressurized feed air having a first set pressure which is higher than the operating pressure of the intermediate pressure column;   an adsorption and purification step in which impurities are adsorbed and removed from the pressurized feed air to obtain a pressurized purified air;   a combining step for a circulating air in which the pressurized purified air and the below-described pressurized returned air are combined to obtain a circulating air;   a cooling step in which a first branch air stream of the two divided circulating air is cooled at a first set temperature to obtain an air to be introduced into the intermediate pressure column, and a second branch air stream is cooled at a second set temperature which is higher than the first set temperature to obtain an air for expansion;   an expansion step in which the air for expansion is adiabatically expanded at a second set pressure which is lower than the first set pressure to obtain a low-temperature air;   a step for introducing a part of the low-temperature air into the intermediate pressure column;   a warming step in which the temperature of the remainder of the low-temperature air is recovered to obtain a returned air;   a circulating compression step in which the returned air is pressurized to obtain the pressurized returned air; and   a step for introducing an air to be introduced into the intermediate pressure column into the intermediate pressure column.

TECHNICAL FIELD

The present invention relates to an air liquefaction separation method and apparatus, and more particularly to an air liquefaction separation method and apparatus in which at least liquid oxygen is collected as a product by a cryogenic separation of a compressed, purified and cooled feed air in an intermediate pressure column and in a low pressure column.

BACKGROUND ART

When oxygen, nitrogen and argon are produced industrially, they are generally produced by a so-called cryogenic air liquefaction separation apparatus, which uses air as a source and in which separation process is performed in a double rectifying column composed of an intermediate pressure column and a low pressure column. By the cryogenic air liquefaction separation apparatus, about 5% of the products can be produced as liquid oxygen, liquid nitrogen and liquid argon. However, when still more liquid products are to be produced, the addition of a liquefaction process is required

The liquefaction process is a process in which a feed air, a nitrogen gas or the like is compressed, circulated and adiabatically expanded to generate cold. For each of the processes, many techniques are disclosed (see, for example, Patent Literature 1).

In such a liquefaction process, a circulating fluid in a partially liquefied state is provided into a distillation column, and a thermally equivalent liquid product is collected. Compared to a nitrogen circulating liquefaction process in which a low pressure and/or intermediate pressure nitrogen gas is compressed into a circulating fluid, an air circulating liquefaction process in which a part of a higher pressure feed air is compressed into a circulating fluid is basically a competitive process in which the amount of power consumption for compressing a circulating fluid is small.

However, when the amount of product in liquid, particularly the amount of liquid nitrogen is large, since the liquefaction rate of a feed air provided in the intermediate pressure column in the air circulating liquefaction process increases, it becomes difficult to control due to decrease in the distillation efficiency. On the other hand, in a nitrogen circulating liquefaction process, since the process is a process in which liquid nitrogen equivalent to a liquid product are provided in the intermediate pressure column, the distillation efficiency in the intermediate pressure column do not decrease even when the amount of product in liquid is large. In other words, when the amount of product in liquid is relatively small, the air circulating liquefaction process in which the power consumption is smaller has an advantage over the nitrogen circulating liquefaction process, and when the amount of product in liquid is relatively large, only the nitrogen circulating liquefaction process is available.

Processes are known in which an air circulating process is used for a single rectifying column process (see, for example, Patent Literatures 2, 3 and 4). In any of the above processes, air is circulated in the process in such a way that a part of feed air having the same operating pressure as in the single rectifying column is circulated and warmed to a ambient temperature, then introduced into a feed air compressor to compress the air in combination with the feed air introduced from the atmosphere. In these processes, although the circulating air does not contain water vapor and carbon dioxide, the circulating air is circulating also in a purifying apparatus. Therefore, the purifying adsorption apparatus was unnecessarily upsized.

Further, a process is known in which an air circulating liquefaction process is used for the double rectifying column (see, for example, Patent Literatures 5 and 6). For example, a feed air is pressurized up to 460 kPa (This pressure is indicated at pressure gauge. Here in after shown “kPaG”.) by using a compressor, and the air is purified and then introduced into a circulating air compressor in combination with a part of a circulating air which is processed in an expansion turbine. The air combined with the circulating air is then pressurized up to a required pressure. The circulating air is cooled to a predetermined temperature by a heat exchanger, then introduced into an expansion turbine to generate a cold which is needed for operating an apparatus. A part of circulating air which is processed in an expansion turbine is introduced into an intermediate pressure column, and the remainder is introduced into a circulating compressor in combination with the feed air. In this process, the operating pressure of the intermediate pressure column is about 480 kPaG, which is nearly equal to the discharge pressure of the expansion turbine and the operating pressure of the purifying apparatus.

A process is also known which uses an air liquefaction separation apparatus which collects oxygen as a product, wherein the ratio of the amount of liquid oxygen collected is changeable (see, for example, Patent Literature 7 and 8). For example, a fluid from the intermediate pressure column is introduced into a downstream side of a purifying apparatus to pressurize the fluid in combination with the feed air. A process is also known in which a fluid from an intermediate pressure column is compressed in combination with the feed air by a compressor at a higher pressure than the operating pressure of the intermediate pressure column (see, for example, Patent Literature 9). However, in this process, since a circulating fluid is also processed in a cooling apparatus and a purifying adsorption equipment, a lot of processing power is needed for these processes.

PRIOR ART LITERATURES Patent Literatures

-   Patent Literature 1 JP 3213846 B -   Patent Literature 2 JP 56-034787 A -   Patent Literature 3 JP 60-044584 A -   Patent Literature 4 JP 54-095552 U -   Patent Literature 5 JP 06-159929 A -   Patent Literature 6 JP 06-159930 A -   Patent Literature 7 JP 10-054657 A -   Patent Literature 8 JP 10-054658 A -   Patent Literature 9 JP 06-300435 A

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

As described above, many proposals have been made about a liquefaction process. In the air circulating liquefaction process, the improvement of the efficiency of the process is a main purpose, and the reduction of the apparatus cost is not yet sufficient.

Accordingly, the purpose of the present invention is to provide an air liquefaction separation method and apparatus which can lower the cost of the apparatus used in the air circulating liquefaction process in which at least liquid oxygen is collected as a product.

Means for Solving the Problems

In order to attain the above object, the first constitution of the present invention is an air liquefaction separation method in which at least liquid oxygen is collected as a product by a cryogenic distillation of a compressed, purified and cooled feed air in an intermediate pressure column and in a low pressure column, the method including:

a feed air compression step in which the whole amount of a feed air is pressurized up to a first set pressure which is higher than the operating pressure of the intermediate pressure column to obtain a pressurized feed air;

an adsorption and purification step in which impurities are adsorbed and removed from the pressurized feed air to obtain a pressurized purified air;

a combining step for a circulating air in which the pressurized purified air and the below-described pressurized returned air are combined to obtain a circulating air;

a cooling step in which a first branch air stream of the two divided circulating air is cooled at a first set temperature to obtain an air to be introduced into the intermediate pressure column, and a second branch air stream is cooled at a second set temperature which is higher than the first set temperature to obtain an air for expansion;

an expansion step in which the air for expansion is adiabatically expanded at a second set pressure which is lower than the first set pressure to obtain a low-temperature air;

a step for introducing a part of the low-temperature air into the intermediate pressure column;

a warming step in which the temperature of the remainder of the low-temperature air is recovered to obtain a returned air;

a circulating compression step in which the returned air is pressurized to obtain the pressurized returned air; and

a step for introducing an air to be introduced into the intermediate pressure column into the intermediate pressure column.

The second constitution of the present invention is an air liquefaction separation method in which at least liquid oxygen is collected as a product by a cryogenic distillation of a compressed, purified and cooled feed air in an intermediate pressure column and in a low pressure column, the method including:

a feed air compression step in which the whole amount of a feed air is pressurized up to a first set pressure which is higher than the operating pressure of the intermediate pressure column to obtain a pressurized feed air;

an adsorption and purification step in which impurities are adsorbed and removed from the pressurized feed air to obtain a pressurized purified air;

a combining step for a circulating air in which the pressurized purified air and the below-described pressurized returned air are combined to obtain a circulating air;

a cooling step in which a first branch air stream of the three divided circulating air is cooled at a first set temperature to obtain an air to be introduced into the intermediate pressure column, a second branch air stream is cooled at a second set temperature which is higher than the first set temperature to obtain an air for cold expansion, and further, a third branch air stream is cooled at a third set temperature which is higher than the second set temperature to obtain an air for warm expansion;

a first expansion step in which the air for cold expansion is adiabatically expanded at a second set pressure which is lower than the first set pressure to obtain a first low-temperature air;

a second expansion step in which the air for warm expansion is adiabatically expanded at the second set pressure to obtain a second low-temperature air whose temperature is higher than the first set temperature;

a step for introducing a part of the first low-temperature air into the intermediate pressure column;

a warming step in which the temperatures of the remainder of the first low-temperature air and the second low-temperature air are recovered to obtain a returned air;

a circulating compression step in which the returned air is pressurized to obtain the pressurized returned air; and

a step for introducing an air to be introduced into the intermediate pressure column into the intermediate pressure column.

Further, the first constitution or the second constitution includes a circulating air pressurizing step in which the circulating air is pressurized at a pressure which is higher than the first set pressure.

The third constitution of the present invention is an air liquefaction separation apparatus in which at least liquid oxygen is collected as a product by a cryogenic distillation of a compressed, purified and cooled feed air in an intermediate pressure column and in a low pressure column, the apparatus including:

a feed air compressor in which the whole amount of a feed air is pressurized up to a first set pressure which is higher than the operating pressure of the intermediate pressure column to obtain a pressurized feed air;

an adsorption apparatus in which impurities are adsorbed and removed from the pressurized feed air to obtain a pressurized purified air;

a combining pipeline for a circulating air in which the pressurized purified air and the below-described pressurized returned air are combined to obtain a circulating air;

a main heat exchanger in which a first branch air stream of the two divided circulating air is cooled at a first set temperature to obtain an air to be introduced into the intermediate pressure column, and a second branch air stream is cooled at a second set temperature which is higher than the first set temperature to obtain an air for expansion;

an expansion turbine in which the air for expansion is adiabatically expanded at a second set pressure which is lower than the first set pressure to obtain a low-temperature air;

a pipeline for introducing a part of the low-temperature air into the intermediate pressure column;

a circulating compressor in which the temperature of the remainder of the low-temperature air is recovered by the main heat exchanger to obtain a returned air and the returned air is pressurized to obtain the pressurized returned air; and

a pipeline for introducing an air to be introduced into the intermediate pressure column into the intermediate pressure column.

Further, the fourth constitution of the present invention is an air liquefaction separation apparatus in which at least liquid oxygen is collected as a product by a cryogenic distillation of a compressed, purified and cooled feed air in an intermediate pressure column and in a low pressure column, the apparatus including:

a feed air compressor in which the whole amount of a feed air is pressurized up to a first set pressure which is higher than the operating pressure of the intermediate pressure column to obtain a pressurized feed air;

an adsorption apparatus in which impurities are adsorbed and removed from the pressurized feed air to obtain a pressurized purified air;

a combining pipeline for a circulating air in which the pressurized purified air and the below-described pressurized returned air are combined to obtain a circulating air;

a main heat exchanger in which a first branch air stream of the three divided circulating air is cooled at a first set temperature to obtain an air to be introduced into the intermediate pressure column, a second branch air stream is cooled at a second set temperature which is higher than the first set temperature to obtain an air for cold expansion, and further, a third branch air stream is cooled at a third set temperature which is higher than the second set temperature to obtain an air for warm expansion;

a cold expansion turbine in which the air for cold expansion is adiabatically expanded at a second set pressure which is lower than the first set pressure to obtain a first low-temperature air;

a warm expansion turbine in which the air for warm expansion is adiabatically expanded at the second set pressure to obtain a second low-temperature air;

a pipeline for introducing a part of the first low-temperature air into the intermediate pressure column;

a circulating compressor in which the temperatures of the remainder of the first low-temperature air and the second low-temperature air are recovered by the main heat exchanger to obtain a returned air, and the returned air is pressurized to obtain the pressurized returned air; and

a pipeline for introducing an air to be introduced into the intermediate pressure column into the intermediate pressure column.

Further, in the third constitution or the fourth constitution, a circulating air compressor in which the circulating air is pressurized at a pressure higher than the first set pressure is included; the circulating air compressor is a brake blower for an expansion turbine set up on the expansion turbine; or braking of the expansion turbine is carried out by a blower, a generator or an oil-hydraulic pump.

Effects of the Invention

By the present invention, since the whole feed air which is conventionally pressurized at a pressure corresponding to the operating pressure of the intermediate pressure column is pressurized at a first set pressure which is higher than the operating pressure of the intermediate pressure column, for example, at a pressure at least about 1.5 times as compared with the operating pressure of the intermediate pressure column, and impurities such as water vapor and carbon dioxide contained in the feed air are adsorbed and removed in this condition, miniaturization of an adsorption apparatus and pipelines therearound is possible as compared with conventional general air liquefaction separation apparatus. Since the partial pressure of the water vapor contained in the feed air becomes relatively small, the needed amount of the adsorbent for adsorbing and removing moisture can be reduced and at the same time, the energy needed for the regeneration of the adsorbent can also be reduced. Therefore, the apparatus cost or the like can be reduced with about the same consumed power source.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a systematic diagram of an air liquefaction separation apparatus showing the first embodiment of the present invention.

FIG. 2 is a partial systematic diagram of an air liquefaction separation apparatus showing the second embodiment of the present invention.

FIG. 3 is a partial systematic diagram of an air liquefaction separation apparatus showing the third embodiment of the present invention.

FIG. 4 is a partial systematic diagram of an air liquefaction separation apparatus showing the fourth embodiment of the present invention.

FIG. 5 is a partial systematic diagram of an air liquefaction separation apparatus showing the fifth embodiment of the present invention.

FIG. 6 is a partial systematic diagram of an air liquefaction separation apparatus showing the sixth embodiment of the present invention.

MODES FOR CARRYING OUT THE INVENTION

The air liquefaction separation apparatus shown as the first embodiment in FIG. 1 is an apparatus in which, by a cryogenic distillation of a compressed, purified and cooled feed air in an intermediate pressure column 11 and in a low pressure column 12, liquid oxygen LO₂, liquid crude argon LAr and liquid nitrogen LN₂ as liquid products are collected, as well as oxygen gas GO₂ and nitrogen gas GN₂ as gas products are collected, and which has, as main component devices, a feed air compressor 13, an adsorption apparatus 14, a circulating compressor 15, a main heat exchanger 16, an expansion turbine 17, a main condenser 18, a crude argon column 19, an argon condenser 20 and a subcooler 21.

First, the whole amount of a feed air is introduced into a feed air compression step in which the air is pressurized by the feed air compressor 13 at a first set pressure which is higher than the operating pressure of the intermediate pressure column 11 to obtain a pressurized feed air. The pressurized feed air is cooled in a cooler 13 a, and condensed water is separated from the air by a drain separator 13 b. The air is then introduced into the adsorption apparatus 14 which carries out an adsorption and purification step. In the adsorption apparatus 14, impurities such as water vapor and carbon dioxide contained in the feed air are adsorbed and removed by an adsorbent, and the pressurized feed air is purified to obtain a pressurized purified air. The pressurized purified air is cooled in a cooler 14 a, passes through a pipeline 51 a which is one of constituents of a combining pipeline for a circulating air 51, and combines with a pressurized returned air which is discharged from a circulating compressor 15 to a pipeline 51 b which is other combining pipeline to be carried out a combining step for a circulating air to obtain a circulating air which flows in a pipeline 51 c.

The circulating air in the pipeline 51 c is divided into two streams of a first branch air stream in the pipeline 52, and a second branch air stream in the pipeline 53 and are introduced into a main heat exchanger 16 which carries out a cooling step. The first branch air stream is cooled at a first set temperature in the main heat exchanger 16 and released from the cold end of the heat exchanger 16 into a pipeline 54 to obtain an air to be introduced into the intermediate pressure column. The pressure of the air to be introduced into the intermediate pressure column is reduced at a pressure corresponding to the operating pressure of an intermediate pressure column 11 at a valve 31, and introduced into the lower part of the intermediate pressure column 11 from a pipeline 55 in a state in which most of the air is liquefied.

The second branch air stream in the pipeline 53 is cooled in a cooling step in the main heat exchanger 16 at a second set temperature which is higher than the first set temperature, and taken out by a pipeline 56 before reaching the cold end of the main heat exchanger 16 to obtain an air for expansion, which is introduced into an expansion turbine 17. The air for expansion is, in the expansion turbine 17, subjected to an expansion step in which the air is adiabatically expanded at a second set pressure which is lower than the first set pressure to obtain a low-temperature air in a pipeline 57. The low-temperature air in the pipeline 57 is divided into a pipeline 58 and a pipeline 59. The low-temperature air branched into the pipeline 59 is introduced as an ascending vapor into the lower part of the intermediate pressure column 11 from a pipeline 60 via a valve 32.

The remainder of the low-temperature air branched into the pipeline 58 is introduced into the cold end of the main heat exchanger to be subjected to a warming step, and heat-exchanged with the first branch air stream and the second branch air stream to cool each of the branch air streams at a predetermined temperature. At the same time, the temperature of the remainder of the low-temperature air is warmed to the ambient temperature to obtain a returned air in a pipeline 61. The returned air is aspirated by the circulating compressor 15 to be subjected to a circulating compression step, pressurized at a pressure corresponding to that of the pressurized purified air. Then, the air is discharged into the pipeline 51 b and combined with the pressurized purified air in the pipeline 51 a to obtain the circulating air in the pipeline 51 c.

The feed air introduced into the lower part of the intermediate pressure column 11 from the pipeline 55 and the pipeline 60 is separated into an intermediate pressure nitrogen-enriched gas at the top of the intermediate pressure column and an oxygen-enriched liquid at the bottom of the intermediate pressure column by the distillation at the intermediate pressure column 11. The oxygen-enriched liquid is taken out from the bottom of the intermediate pressure column by a pipeline 62, cooled by a subcooler 21, and then divided into a pipeline 63 and a pipeline 64. The pressure of the oxygen-enriched liquid in the pipeline 64 is reduced at a pressure corresponding to the operating pressure of the low pressure column 12 at a valve 33, and then passes through a pipeline 65 to be introduced into the intermediate part of the low pressure column 12 as a reflux liquid.

The pressure of the oxygen-enriched liquid which flows in the pipeline 63 is reduced at a valve 34, and then introduced into an argon condenser 20 set up on the upper of the crude argon column 19. The oxygen-enriched gas vaporized at the argon condenser 20 is introduced as an ascending vapor into the intermediate part of the low pressure column 12 through a pipeline 66. The oxygen portion of the oxygen-enriched liquid and the oxygen-enriched gas, which are introduced into the low pressure column 12, is concentrated at the bottom of the low pressure column by the distillation at the low pressure column 12 to obtain a low pressure liquid oxygen. A part of this low pressure liquid oxygen is taken out by a pipeline 67, cooled at the subcooler 21, and then collected as a product liquid oxygen from a pipeline 68.

The intermediate pressure nitrogen-enriched gas at the top of the intermediate pressure column is introduced into a main condenser 18 disposed at the bottom of the low pressure column through a pipeline 69, heat exchanged indirectly with the low pressure liquid oxygen, which vaporizes the low pressure liquid oxygen to obtain a low pressure oxygen gas. At the same time, the intermediate pressure nitrogen-enriched gas is liquefied and a liquid nitrogen is obtained. A part of this liquid nitrogen is returned as a reflux liquid into the top part of the intermediate pressure column 11 through a pipeline 70. The remainder of the liquid nitrogen passes through a pipeline 71, cooled at the subcooler 21, and then a part of the remainder is divided into a pipeline 72 to be collected as a product liquid nitrogen. The pressure of most of the liquid nitrogen is reduced at a pressure corresponding to the operating pressure of the low pressure column 12 at a valve 35, and then the liquid nitrogen passes through a pipeline 73 and introduced as a reflux liquid into the top part of the low pressure column 12.

Further, an argon-enriched gas fluid (feed argon) is taken out from the intermediate part of the low pressure column 12 into a pipeline 74, introduced into the lower part of the crude argon column 19. A crude argon gas in which argon is concentrated is separated at the top of the crude argon column by a distillation at the crude argon column 19, and a liquid in which the concentration of argon is reduced is separated at the bottom of the crude argon column. The liquid in which the concentration of argon is reduced is taken out from the bottom of the crude argon column into a pipeline 75 and returned as a descending liquid into the intermediate part of the low pressure column 12.

The crude argon gas at the top part of the crude argon column is introduced into the argon condenser 20 via a pipeline 76 and liquefied by heat exchange with the oxygen-enriched liquid at the argon condenser 20 to obtain a liquid crude argon. A part of this liquid crude argon is collected as a product liquid crude argon from a pipeline 77.

The remainder of the liquid crude argon passes through a pipeline 78 and introduced as a reflux liquid into the upper part of the crude argon column 19.

The low pressure nitrogen gas which is concentrated at the top part of the low pressure column by the distillation at the low pressure column 12 is taken out by a pipeline 79, introduced into the subcooler 21 and used as the cooling source of each of the above-mentioned liquids, and then introduced into the cold end of the main heat exchanger 16 via a pipeline 80. A part of the low pressure oxygen gas which is vaporized at the main condenser 18 is taken out by a pipeline 81, introduced into the cold end of the main heat exchanger 16. Most of the remainder of the low pressure oxygen gas is an ascending vapor in the low pressure column 12. Further, a part of the ascending vapor in the low pressure column 12 is taken out by a pipeline 82 as a waste gas WG from the upper middle part of the low pressure column 12, which is a cooling source of the subcooler 21. Then, the waste gas is introduced into the cold end of the main heat exchanger 16.

The low pressure nitrogen gas, low pressure oxygen gas and waste gas are heat exchanged with each of the branch air streams introduced into the warm end of the main heat exchanger 16, and warmed at an ambient temperature to recover the temperature. Then, the low pressure nitrogen gas is collected as a product nitrogen gas from a pipeline 83; the low pressure oxygen gas is collected as a product oxygen gas from a pipeline 84; and the waste gas is taken out by a pipeline 85, and then used as a regenerated gas in the adsorption apparatus 14 or the like.

In an air liquefaction separation apparatus formed in such a way, the first set pressure of the pressurized feed air in which the feed air is pressurized in the feed air compressor 13 is set at a pressure higher than the operating pressure of the intermediate pressure column 11. Generally, since the operating pressure of the intermediate pressure column 11 in a double rectifying column including a intermediate pressure column 11, a low pressure column 12, and a main condenser 18 is about 500 kPaG, the pressure of a low temperature air introduced from a pipeline 60 into the lower part of the intermediate pressure column 11 is also about the same pressure as the operating pressure, and the pressure of the returned air which flows in a pipeline 61 is also about 500 kPaG which is about the same pressure as the operating pressure of the intermediate pressure column 11, when the compression ratio of the circulating compressor 15 in which the circulating air is pressurized is 1.5 to 1.8, the pressure of a pressurized feed air having the same pressure as the discharge pressure of the circulating compressor 15, that is, the first set pressure is about 750 kPaG (500 kPaG×1.5) to 900 kPaG (500 kPaG×1.8).

Therefore, in the present embodiments, since the operating pressure of the adsorption apparatus 14 which removes impurities from a feed air is about 1.5 times as compared with the pressure of a conventional normal air liquefaction separation apparatus, the miniaturization of the adsorption apparatus body and pipelines therearound in the adsorption apparatus 14 is possible and the cost of the apparatus can be reduced. That is, since the cylinder diameter of the adsorption column of the adsorption apparatus 14 can be reduced as compared with a conventional adsorption apparatus, the cost of the material of the adsorption cylinder is reduced. Since the amount of water vapor accompanied by the feed air is reduced, the amount of alumina gel needed for the adsorptive removal of water vapor can be reduced. The equipment cost of the adsorption apparatus as a whole can, therefore, be greatly reduced. Since the amount of water vapor contained in the feed air is reduced, cooling the feed air at a low temperature is not necessary, and a cost needed for a cooling equipment can be reduced.

In the description of the other embodiments of the present invention as described below, the same component as the component of the air liquefaction separation apparatus as shown in the first embodiment is represented by the same reference numeral and the detail description thereof is omitted. Since the constitutions about the intermediate pressure column and the low pressure column can adopt the same constitution of the first embodiment, the illustration and the explanation thereof are omitted.

The air liquefaction separation apparatus as shown in the second embodiment in FIG. 2 is formed such that the circulating compressor 15 is a multistage compressor having a first compressor stage 15 a and a second compressor stage 15 b; a pressurized returned air discharged from the first compressor stage 15 a is combined with a pressurized purified air to obtain a circulating air; the circulating air is subjected to a circulating air pressurizing step in the second compressor stage 15 b of the circulating compressor 15 to obtain a further pressurized high pressure circulating air, and then subjected to a second circulating air pressurizing step in a brake blower 22 of an expansion turbine 17 to be further pressurized at a higher pressure.

That is, a pressurized purified air in which the feed air in which the whole amount of the feed air is pressurized at the first set pressure in a feed air compressor 13 is purified in the adsorption apparatus 14 passes through a pipeline 51 a of a combining pipeline for a circulating air 51, combined with a pressurized returned air in a pipeline 51 b discharged from the first compressor stage 15 a and cooled by an after-cooler to a pipeline 51 c, and pressurized at a higher pressure than the first set pressure in the second compressor stage 15 b to obtain a high pressure circulating air.

A part of the high pressure circulating air discharged from the circulating compressor 15 is branched into the pipeline 52, introduced into the main heat exchanger 16 to be cooled at a first set temperature in the same way as described above, and introduced via a pipeline 54, a valve 31 and a pipeline 55 into the lower part of the intermediate pressure column 11 in a state in which most of the air is liquefied.

The remainder of the high pressure circulating air branched into the pipeline 53 is introduced into the brake blower 22 of the expansion turbine 17 and further pressurized at a high pressure, then introduced into the main heat exchanger 16 via a pipeline 86, cooled at a second set temperature which is higher than the first set temperature, and taken out by a pipeline 56 before reaching the cold end of the main heat exchanger 16 to obtain an air for expansion, which is introduced into an expansion turbine 17. The air for expansion is, in the expansion turbine 17, adiabatically expanded at a second set pressure which is lower than the first set pressure to obtain a low-temperature air in a pipeline 57. A part of this low-temperature air is branched into a pipeline 59 and introduced into the lower part of the intermediate pressure column via a valve 32 and a pipeline 60. The remainder of the low-temperature air is branched into a pipeline 58 and introduced into the cold end of the main heat exchanger 16. The temperature of the air is recovered to obtain a returned air in a pipeline 61, and the air is aspirated by the first compressor stage 15 a of the circulating compressor 15 to be circulated.

In this way, by pressurizing the circulating air in a circulating air pressurizing step to obtain a still higher pressure circulating air, the expansion ratio of the expansion turbine 17 can be increased, and the amount of generated cold can be increased.

The air liquefaction separation apparatus as shown in the third embodiment in FIG. 3 has, as an expansion turbine which carries out an expansion step, a cold expansion turbine 17 a in which an air for expansion (an air for cold expansion) having the second set temperature which is relatively low is adiabatically expanded and a warm expansion turbine 17 b in which an air for expansion (an air for warm expansion) having a third set temperature which is relatively higher than the second set temperature is adiabatically expanded, and at the same time, as the brakes for both the expansion turbines 17 a and 17 b, a brake blower for a cold expansion turbine 22 a and a brake blower for a warm expansion turbine 22 b are provided respectively.

In the same manner as in the second embodiment, a pressurized purified air and a pressurized returned air are combined, and then pressurized in the second compressor stage 15 b of the circulating compressor 15 to obtain a high pressure circulating air. This air is divided into a first branch air stream in a pipeline 52 and a second branch air stream in a pipeline 53. The second branch air stream in the pipeline 53 is further pressurized in the brake blower for a cold expansion turbine 22 a, introduced into the main heat exchanger 16 from a pipeline 86, taken out by a pipeline 56 in a state in which the air is cooled at the second set temperature to obtain an air for cold expansion. This air for cold expansion is subjected to a first expansion step in the cold expansion turbine 17 a and adiabatically expanded at the second set pressure to obtain a first low-temperature air having a temperature near the first set temperature.

A part of the first low-temperature air is branched from a pipeline 57 to a pipeline 59 and introduced into the lower part of the intermediate pressure column 11 via a valve 32 and a pipeline 60. The remainder of the first low-temperature air branched into a pipeline 58 is introduced into the cold end of the main heat exchanger 16 and the temperature of the air is recovered to obtain a returned air in a pipeline 61, and the air is aspirated by the first compressor stage 15 a of the circulating compressor 15 to be circulated in the same way as described above.

On the other hand, the first branch air stream in the pipeline 52 is further pressurized in a brake blower for a warm expansion turbine 22 b, introduced from a pipeline 87 to the main heat exchanger 16, cooled at a third set temperature which is higher than the second set temperature, and a part of the air is branched as a third air stream and taken out by a pipeline 88 to obtain an air for warm expansion. This air for warm expansion is subjected to a second expansion step in a warm expansion turbine 17 b and adiabatically expanded at the second set pressure to obtain a second low-temperature air having a temperature which is higher than the first set temperature and lower than the third set temperature. The air is introduced into the main heat exchanger 16 from a pipeline 89 whose position is corresponding to the temperature of the second low-temperature air, combined with the first low-temperature air whose temperature is in recovery and released into a pipeline 61 to obtain a returned air and circulated in a circulating compressor 15. The remainder of the first branch air stream is cooled in the main heat exchanger 16 at the first set temperature and introduced into the intermediate pressure column 11 via a pipeline 54, a valve 31 and a pipeline 55.

In this way, by dividing the expansion step into two steps of warm and cold steps, an adiabatic expansion by an expansion turbine can be carried out efficiently and the feed air introduced into the intermediate pressure column 11 can be effectively cooled.

The air liquefaction separation apparatus as shown in the fourth embodiment in FIG. 4 is the same apparatus as in the third embodiment except that the circulating compressor 15 is a multistage compressor having a first compressor stage 15 a, a second compressor stage 15 b and a third compressor stage 15 c. The circulating air which is pressurized at the second compressor stage 15 b of the circulating compressor 15 is, in the same manner as above, divided into a first branch air stream in a pipeline 52 and a second branch air stream in a pipeline 53. The first branch air stream is further pressurized in the brake blower for a warm expansion turbine 22 b, introduced from a pipeline 87 into the main heat exchanger 16, and a part of the air is branched as a third branch air stream into a pipeline 88 at the third set temperature to obtain an air for warm expansion and introduced into a warm expansion turbine 17 b. The air is adiabatically expanded at the second set pressure in the warm expansion turbine 17 b to obtain the same second low-temperature air as above, and then introduced from a pipeline 89 into the main heat exchanger 16 and the temperature of the air is recovered, then the air is circulated in the circulating compressor 15 via a pipeline 61.

On the other hand, the second branch air stream in the pipeline 53 is further pressurized at a high pressure by a third compressor stage 15 c and a brake blower for a cold expansion turbine 22 a, then introduced into the main heat exchanger 16 via a pipeline 86, taken out by a pipeline 56 at the second set temperature to obtain an air for cold expansion. The air is adiabatically expanded by a cold expansion turbine 17 a at the second set pressure to obtain a first low-temperature air having a temperature near the first set temperature. A part of the first low-temperature air in a pipeline 57 is introduced into the lower part of the intermediate pressure column 11 via a pipeline 59, a valve 32 and a pipeline 60. The remainder of the first low-temperature air is introduced into the main heat exchanger 16 from a pipeline 58, combined with the second low-temperature air. The temperature of the air is recovered to obtain a returned air in a pipeline 61 and the air is aspirated by the circulating compressor 15 to be circulated.

The air liquefaction separation apparatus as shown in the fifth embodiment in FIG. 5 is the same apparatus as in the fourth embodiment except that a generator 23 is installed in place of the brake blower for a cold expansion turbine 22 a and braking of the cold expansion turbine 17 a is carried out by the generator 23, and that the second branch air stream which is branched into a pipeline 53 and pressurized in the third compressor stage 15 c of the circulating compressor 15 is introduced from a pipeline 90 into the main heat exchanger 16 with the pressure as is. As described above, for the brake of the expansion turbine, a generator brake or an oil brake other than blower brakes can be employed.

The air liquefaction separation apparatus as shown in the sixth embodiment in FIG. 6 is formed such that a pressurized purified air which is pressurized at a first set pressure which is higher than the operating pressure of the intermediate pressure column 11 in a feed air compressor 13 and purified in a adsorption apparatus 14, and a pressurized returned air which is pressurized in a circulating compressor 15 and further pressurized in a brake blower for a cold expansion turbine 22 a and a brake blower for a warm expansion turbine 22 b are combined.

That is, the pressurized purified air released from the adsorption apparatus 14 to a pipeline 91 is divided into a pipeline 92 and a pipeline 93 which constitute a combining pipeline for a circulating air. On the other hand, the pressurized returned air in which the returned air in the pipeline 61 is pressurized in the circulating compressor 15 is divided into a pipeline 94 flow to the brake blower for a cold expansion turbine 22 a and a pipeline 95 flow to the brake blower for a warm expansion turbine 22 b.

A pressurized returned air which is divided into a pipeline 94 and further pressurized in the brake blower for a cold expansion turbine 22 a is passed through a pipeline 96 which constitutes the combining pipeline for a circulating air, combined with the pressurized purified air from the pipeline 92, introduced into the main heat exchanger 16 through a pipeline 97, cooled at a second set temperature and taken out by a pipeline 56 to obtain the air for cold expansion, and the air is introduced into a cold expansion turbine 17 a.

The pressurized returned air which is divided into a pipeline 95 and further pressurized in the brake blower for a warm expansion turbine 22 b is passed through a pipeline 98 which constitutes the combining pipeline for a circulating air, combined with a pressurized purified air from the pipeline 93, introduced into the main heat exchanger 16 through a pipeline 99. A part of the air is taken out by a pipeline 88 at the point when the air is cooled at a third set temperature to obtain an air for warm expansion and the air is introduced into the warm expansion turbine 17 b. The remainder of the air is cooled at a first set temperature to obtain an air to be introduced into the intermediate pressure column in a pipeline 54 and the air is introduced into the intermediate pressure column 11.

In each of the embodiments, although an example in which liquid oxygen LO₂, liquid crude argon LAr and liquid nitrogen LN₂ are collected as liquid products is shown, the present invention is also applicable to an air liquefaction separation apparatus in which only liquid oxygen LO₂ is collected as a liquid product, and a combination of liquid oxygen LO₂ and liquid crude argon LAr and a combination of liquid oxygen LO₂ and liquid nitrogen LN₂ are also possible. For the circulating compressor, a compressor having 4 or more compressor stages can be used depending on the suction pressure, the discharge pressure and the throughput.

Next, by using the air liquefaction separation apparatus as shown in the third embodiment, a specific example is explained in a case in which a liquid oxygen 1500 Nm³/h, a liquid nitrogen 1000 Nm³/h and a liquid argon 50 Nm³/h are collected. [Nm³/h] means a flow rate per 1 hour at a temperature of 0° C. and a pressure of 1 atmosphere.

First, the whole amount of a feed air (8800 Nm³/h) is pressurized at about 850 kPaG by a feed air compressor 13, and then introduced into an adsorption apparatus 14 which uses an activated alumina gel and zeolite, where impurities such as water vapor and carbon dioxide contained in the feed air are adsorbed and removed and the feed air is purified. The purified feed air (pressurized purified air) is introduced between a first compressor stage 15 a and a second compressor stage 15 b of a circulating compressor 15, combined with a pressurized returned air (12800 Nm³/h) discharged from the first compressor stage 15 a and pressurized at 2700 kPaG in the second compressor stage 15 b to obtain a circulating air.

A part of the circulating air (a first branch air stream 7700 Nm³/h) is pressurized at 4000 kPaG by a brake blower for a warm expansion turbine 22 b and then introduced into a main heat exchanger 16. A part of the first branch air stream (a third branch air stream 4000 Nm³/h) is taken out from the main heat exchanger 16 at the point when the air is cooled at a third set temperature in the main heat exchanger 16, introduced into a warm expansion turbine 17 b to be adiabatically expanded at a second set temperature to obtain a second low-temperature air. The remainder of the first branch air stream (3700 Nm³/h) is cooled at the first set temperature in the main heat exchanger 16. The pressure of the air is reduced at a pressure corresponding to the intermediate pressure column at a valve 31, and then introduced into the intermediate pressure column 11 through a pipeline 55.

The remainder of the circulating air (a second branch air stream 13900 Nm³/h) is pressurized at 4000 kPaG by the brake blower for a cold expansion turbine 22 a, introduced into the main heat exchanger 16. The air is cooled at a second set temperature by the main heat exchanger 16, then introduced into a cold expansion turbine 17 a and adiabatically expanded to obtain a first low-temperature air. A part of the first low-temperature air (8800 Nm³/h) is introduced into the main heat exchanger 16 and combined with the second low-temperature air. The temperature of the first low-temperature air is recovered by being used as a cooling source of the feed air (a circulating air) to obtain a returned air. The remainder of the first low-temperature air (5100 Nm³/h) is introduced into the lower part of the intermediate pressure column 11 through a valve 32 and a pipeline 60.

The feed air introduced into the intermediate pressure column 11 (3700 Nm³/h from the pipeline 55 and 5100 Nm³/h from the pipeline 60) is cryogenically distilled in the intermediate pressure column 11, the low pressure column 12 and the crude argon column 19 to obtain liquid oxygen 1500 Nm³/h, liquid nitrogen 1000 Nm³/h, liquid argon 50 Nm³/h as liquid products, oxygen gas and nitrogen gas as gas products and waste gases.

The flow rate, temperature, pressure and oxygen composition of the gases and liquids which flow in the main pipelines are shown in Table 1. Main specifications of adsorption apparatuses comparing the adsorption apparatus of the present embodiment with a conventional adsorption apparatus are shown in Table 2. The amount of activated alumina and below in Table 2 are relative amounts with those of conventional apparatus being 100.

TABLE 1 Pipeline Flow rate Temperature Pressure Oxygen composition No. (Nm³/h) (K) (kPaG) (—)  51a 8800 313 850   0.21 52 7700 313 2700 (Air composition) 87 7700 313 4000 54 3700 99 3900 53 13900 313 2700 86 13900 313 4000 60 5100 104 500 61 12800 308 498 68 1500 94 55 ± H >0.995 72 1000 96 500 ± H  <1 ppm 77 50 89 25 ± H <0.02 (H: Liquid pressure head)

TABLE 2 Conventional Embodiment art Feed air amount (Nm³/h) 8800 8800 Operating pressure (kPaG) 850 500 Adsorption temperature (K) 313 313 Accompanying water amount (kg/h) 88 55 Activated alumina amount 63 100 Adsorption apparatus: Cylinder diameter 80 100 Adsorption apparatus: Cost (Material) 64 100 Adsorption apparatus: Cost (Adsorbent) 86 100 Adsorption apparatus: Cost (Total) 93 100

DESCRIPTION OF THE REFERENCE NUMERAL

-   11 intermediate pressure column -   12 low pressure column -   13 feed air compressor -   14 adsorption apparatus -   15 circulating compressor -   15 a first compressor stage -   15 b second compressor stage -   15 c third compressor stage -   16main heat exchanger -   17 expansion turbine -   17 a cold expansion turbine -   17 b warm expansion turbine -   18 main condenser -   19 crude argon column -   20 argon condenser -   21 subcooler -   22 brake blower -   22 a brake blower for a cold expansion turbine -   22 b brake blower for a warm expansion turbine -   23 generator -   51 combining pipeline for a circulating air 

1. An air liquefaction separation method in which at least liquid oxygen is collected as a product by a cryogenic distillation of a compressed, purified and cooled feed air in an intermediate pressure column and in a low pressure column, the method including: a feed air compression step in which the whole amount of a feed air is pressurized up to a first set pressure which is higher than the operating pressure of the intermediate pressure column to obtain a pressurized feed air; an adsorption and purification step in which impurities are adsorbed and removed from the pressurized feed air to obtain a pressurized purified air; a combining step for a circulating air in which the pressurized purified air and the below-described pressurized returned air are combined to obtain a circulating air; a cooling step in which a first branch air stream of the two divided circulating air is cooled at a first set temperature to obtain an air to be introduced into the intermediate pressure column, and a second branch air stream is cooled at a second set temperature which is higher than the first set temperature to obtain an air for expansion; an expansion step in which the air for expansion is adiabatically expanded at a second set pressure which is lower than the first set pressure to obtain a low-temperature air; a step for introducing a part of the low-temperature air into the intermediate pressure column; a warming step in which the temperature of the remainder of the low-temperature air is recovered to obtain a returned air; a circulating compression step in which the returned air is pressurized to obtain the pressurized returned air; and a step for introducing an air to be introduced into the intermediate pressure column into the intermediate pressure column.
 2. An air liquefaction separation method in which at least liquid oxygen is collected as a product by a cryogenic distillation of a compressed, purified and cooled feed air in an intermediate pressure column and in a low pressure column, the method including: a feed air compression step in which the whole amount of a feed air is pressurized up to a first set pressure which is higher than the operating pressure of the intermediate pressure column to obtain a pressurized feed air; an adsorption and purification step in which impurities are adsorbed and removed from the pressurized feed air to obtain a pressurized purified air; a combining step for a circulating air in which the pressurized purified air and the below-described pressurized returned air are combined to obtain a circulating air; a cooling step in which a first branch air stream of the three divided circulating air is cooled at a first set temperature to obtain an air to be introduced into the intermediate pressure column, a second branch air stream is cooled at a second set temperature which is higher than the first set temperature to obtain an air for cold expansion, and further, a third branch air stream is cooled at a third set temperature which is higher than the second set temperature to obtain an air for warm expansion; a first expansion step in which the air for cold expansion is adiabatically expanded at a second set pressure which is lower than the first set pressure to obtain a first low-temperature air; a second expansion step in which the air for warm expansion is adiabatically expanded at the second set pressure to obtain a second low-temperature air whose temperature is higher than the first set temperature; a step for introducing a part of the first low-temperature air into the intermediate pressure column; a warming step in which the temperatures of the remainder of the first low-temperature air and the second low-temperature air are recovered to obtain a returned air; a circulating compression step in which the returned air is pressurized to obtain the pressurized returned air; and a step for introducing an air to be introduced into the intermediate pressure column into the intermediate pressure column.
 3. The air liquefaction separation method according to claim 1, including a circulating air pressurizing step in which the circulating air is pressurized at a pressure which is higher than the first set pressure.
 4. An air liquefaction separation apparatus in which at least liquid oxygen is collected as a product by a cryogenic distillation of a compressed, purified and cooled feed air in an intermediate pressure column and in a low pressure column, the apparatus including: a feed air compressor in which the whole amount of a feed air is pressurized up to a first set pressure which is higher than the operating pressure of the intermediate pressure column to obtain a pressurized feed air; an adsorption apparatus in which impurities are adsorbed and removed from the pressurized feed air to obtain a pressurized purified air; a combining pipeline for a circulating air in which the pressurized purified air and the below-described pressurized returned air are combined to obtain a circulating air; a main heat exchanger in which a first branch air stream of the two divided circulating air is cooled at a first set temperature to obtain an air to be introduced into the intermediate pressure column, and a second branch air stream is cooled at a second set temperature which is higher than the first set temperature to obtain an air for expansion; an expansion turbine in which the air for expansion is adiabatically expanded at a second set pressure which is lower than the first set pressure to obtain a low-temperature air; a pipeline for introducing a part of the low-temperature air into the intermediate pressure column; a circulating compressor in which the temperature of the remainder of the low-temperature air is recovered by the main heat exchanger to obtain a returned air and the returned air is pressurized to obtain the pressurized returned air; and a pipeline for introducing an air to be introduced into the intermediate pressure column into the intermediate pressure column.
 5. An air liquefaction separation apparatus in which at least liquid oxygen is collected as a product by a cryogenic distillation of a compressed, purified and cooled feed air in an intermediate pressure column and in a low pressure column, the apparatus including: a feed air compressor in which the whole amount of a feed air is pressurized up to a first set pressure which is higher than the operating pressure of the intermediate pressure column to obtain a pressurized feed air; an adsorption apparatus in which impurities are adsorbed and removed from the pressurized feed air to obtain a pressurized purified air; a combining pipeline for a circulating air in which the pressurized purified air and the below-described pressurized returned air are combined to obtain a circulating air; a main heat exchanger in which a first branch air stream of the three divided circulating air is cooled at a first set temperature to obtain an air to be introduced into the intermediate pressure column, a second branch air stream is cooled at a second set temperature which is higher than the first set temperature to obtain an air for cold expansion, and further, a third branch air stream is cooled at a third set temperature which is higher than the second set temperature to obtain an air for warm expansion; a cold expansion turbine in which the air for cold expansion is adiabatically expanded at a second set pressure which is lower than the first set pressure to obtain a first low-temperature air; a warm expansion turbine in which the air for warm expansion is adiabatically expanded at the second set pressure to obtain a second low-temperature air; a pipeline for introducing a part of the first low-temperature air into the intermediate pressure column; a circulating compressor in which the temperatures of the remainder of the first low-temperature air and the second low-temperature air are recovered by the main heat exchanger to obtain a returned air, and the returned air is pressurized to obtain the pressurized returned air; and a pipeline for introducing an air to be introduced into the intermediate pressure column into the intermediate pressure column.
 6. The air liquefaction separation apparatus according to claim 4, including a circulating air compressor in which the circulating air is pressurized at a pressure higher than the first set pressure.
 7. The air liquefaction separation apparatus according to claim 6, wherein the circulating air compressor is a brake blower for an expansion turbine set up on the expansion turbine.
 8. The air liquefaction separation apparatus according to claim 4, wherein braking of the expansion turbine is carried out by a blower, a generator or an oil-hydraulic pump.
 9. The air liquefaction separation method according to claim 2, including a circulating air pressurizing step in which the circulating air is pressurized at a pressure which is higher than the first set pressure.
 10. The air liquefaction separation apparatus according to claim 5, including a circulating air compressor in which the circulating air is pressurized at a pressure higher than the first set pressure.
 11. The air liquefaction separation apparatus according to claim 10, wherein the circulating air compressor is a brake blower for an expansion turbine set up on the expansion turbine.
 12. The air liquefaction separation apparatus according to claim 5, wherein braking of the expansion turbine is carried out by a blower, a generator or an oil-hydraulic pump.
 13. The air liquefaction separation apparatus according to claim 6, wherein braking of the expansion turbine is carried out by a blower, a generator or an oil-hydraulic pump.
 14. The air liquefaction separation apparatus according to claim 10, wherein braking of the expansion turbine is carried out by a blower, a generator or an oil-hydraulic pump. 